Several new heterometallic metal-organic frameworks (MOFs) based on tris(dipyrrinato) metalloligands and Ag+ salts are reported. MOFs were prepared systematically to examine the effects of the core metal ion, counteranion, and ligand structure on the topology of the resultant network. The effect of the metal ion (Fe3+ vs Co3+) on MOF structure was generally found to be negligible, thereby permitting the facile synthesis of trimetallic Fe/Co/Ag networks. The choice of anion (e.g., silver salt) was found to have a pronounced effect on the MOF topology. Networks prepared with salts of AgO3SCF3 and AgBF4 reliably formed three-dimensional (10,3) nets, whereas use of AgPF6 and AgSbF6 produced two-dimensional (6,3) honeycomb nets. The topology generated upon formation of the MOF was found to be robust in certain cases, as demonstrated by anion-exchange experiments. Anion exchange was confirmed by X-ray crystallography in a rare set of apparent single-crystal-to-single-crystal transformations. The data presented here strongly suggest that the coordinative ability of the anion does not play a significant role in the observed templating effect. Finally, changes in the length of the tris(dipyrrinato) metalloligand were found to override the anion templating effect, resulting exclusively in two-dimensional (6,3) nets. These studies provide a basis for the rational design of MOF topologies by choice of ligand structure and anion templating effects. Furthermore, the results demonstrate the ability of carefully designed metalloligands to generate MOFs of structure strikingly similar to that of their organic counterparts.
Although free dipyrrins (dipyrromethenes) do not strongly luminesce, certain dipyrrinato complexes of BF2 and zinc(II) are known to be intensely luminescent species. Two new dipyrrinato fluorophores, based on complexes with gallium(III) and indium(III), are described. Using a previously described meso-mesityl-substituted dipyrrin, namely 5-mesityldipyrrin (mesdpm), the complexes [Ga(mesdpm)3] and [In(mesdpm)3] were prepared and structurally characterized. The complexes display the expected octahedral geometry about the metal ions. In some solvents, such as hexanes, the complexes emit green light upon excitation with UV light at room temperature, with quantum yields of 2.4% ([Ga(mesdpm)3]) and 7.4% ([In(mesdpm)3]) and lifetimes in the low nanosecond range. Observations are consistent with assignment to ligand-localized transitions, and this interpretation is further confirmed by density functional calculations described herein. The new complexes are important additions to the widely used family of dipyrrin-based fluorescent species and show that dipyrrinato complexes containing metals other than BF2 and zinc(II) may be useful fluorophores.
New main-group metal dipyrrinato complexes [M(4-pyrdpm)3], where M = Ga3+ or In3+ and 4-pyrdpm is the anion of 5-(4-pyridyl)dipyrrin (4-pyrdpmH), have been synthesized and incorporated into metal-organic frameworks (MOFs) by reacting the dipyrrinato complexes with silver(I) salts. MOFs formed with AgOTf (OTf = O3SCF3) and AgSbF6 gave frameworks with three-dimensional (10,3) and two-dimensional (6,3) topologies, respectively. In contrast, AgPF6 produced both (10,3) and (6,3) network topologies, suggesting that the PF6 anion has little preference for templating (10,3) versus (6,3) frameworks within this system. These findings update an earlier MOF study that examined the role of these anions in templating related heterometallic MOFs which used [Fe(4-pyrdpm)3] and [Co(4-pyrdpm)3] metalloligands. All of the dipyrrin compounds reported here have been characterized by single-crystal X-ray crystallography, including the first crystallographically characterized example of a 1,2,3-unsubstituted free-base dipyrrin, 4-pyrdpmH.
TlI[(C4H9N4)PtII(CN)2] forms a red, crystalline polymorph in which the ions are arranged to form an extended ...Pt...Tl...Pt...Tl... chain (Pt...Tl distance, 3.0978(2) A; Pt-Tl-Pt and Tl-Pt-Tl angles, (171.37(2) degrees ) and a yellow polymorph in which dimers are connected by pairs of Pt...Tl interactions with a Pt...Tl distance of 3.0256(5) A.
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